The present invention relates in general to pulse generators. More specifically, the present invention relates to bipolar pulse generators that provide a high power/energy pulse on a load.
Recent trends in the development of pulse power microwave sources for a variety of applications have been directed to increasing power, efficiency and energy on the load. Transmission line pulse generators with different kinds of fast switches, including light activated photoconductors, can achieve some of the best results in generating high power short duration pulses. For a given limited charging voltage of transmission lines defined by high-current switches, high powered and high energy density transmission lines imply low characteristic impedances. This low range of characteristic impedances, however, frequently causes problems for coupling with typically used load impedances, 50 ohm or higher, for example, radiating impedances, which introduces a problem with efficient high ratio impedance transformation.
Bipolar pulse generators very often have significant advantages compared to unipolar pulse generators, with just one example being UWB radiation. Further, there are many potential applications of bipolar pulse generators, for example in industry, physics and medicine, where very often bipolar pulse generators with time separation between positive and negative sub-pulses are preferable or required. Today, however, there are only various types of high power and high energy unipolar pulse generators (Marx generator and stacked Blumlein generator in various modifications).
For example, a high energy Marx generator with coaxial cable to provide rectangular unipolar pulse is known and described in “A PFN Marx Generator Based on High-Voltage Transmission Lines”, by S. M. Turnbull et al. presented in Meas. Sci. Technol. 11 (2000) N51-N55. Further, a stacked Blumlein generator with a single switch has been proposed in U.S. Pat. No. 2,769,101 issued to R. D. Drosd. This type of generator has been designed and presented in various publications including, for example, “Modeling of Wound Coaxial Blumlein Pulsers”, by Jose O. Rossi et al:, published in IEEE Transactions on Plasma Science”, Vol. 34, No. 5, October 2006, “Design of a 150 kV, 300A, 100 Hz Blumlein Coaxial Pulser for Long Pulse Operation”, presented in IEEE Transactions on Plasma Science”, Vol. 30, No. 5, October 2002. Still further, some modifications of stacked (cascade) Blumlein generators are presented in “A Combined High-Voltage, High-Energy Pulse Generator”, by S. J. MacGregor et al. published in “Meas. Sci. Technol” 5 (1994), pp. 1580-1582, and “A Novel HV Double Pulse Modulator”, published in “Meas. Sci. Technol” 5 (1994), pp. 1407-1408. Finally, another type of high-power generator, namely, a “Multi-Stage Blumlein” is proposed by J. Yampolsky in U.S. Patent Application 2005/0174715 A1, 2005. The content of each of the above-reference documents is incorporated herein by reference. All of the above-referenced generators produce only a unipolar pulse and do not provide voltage (impedance) transformation, with the exception of the proposed multi-stage Blumlein disclosed in U.S. Patent Application 2005/0174715A1, which provides moderate transformation but requires a substantial number of switching devices.
A transmission line “High-Voltage Pulses Generator” has also been described in U.S. Pat. No. 1,098,502 A1 issued to Bosamykin V. S. et al, 1996, which provides bipolar pulse by a single switch. However, the power/energy on load is much less compared to that provided by the above-mentioned unipolar generators. In addition, impedance transformation in the device is low.
The applicant has also previously described a transmission line in U.S. Patent Application 2007/0165839 A1 entitled “Bipolar Pulse Generators With Voltage Multiplication”, which provides a device with a single switch with all of the required voltage/impedance transformation. However, in a stacked configuration with several switches, the energy provided by this type of generator is less compared to the above mentioned Blumlein-based stacked unipolar generators with less number of switches.
Accordingly, there remains a need for a bipolar pulse generator solution based on voltage charged transmission lines, which provides high power and high energy. Further, there remains a need for high power/energy bipolar pulse generator, which can provide voltage/impedance transformation. Still further, there remains a need for a high power/energy bipolar pulse generator with pulse separation between positive and negative sub-pulses.
It would be desirable to provide a bipolar pulse generator that could meet all of the above needs while being implemented in a simple structure, preferably with a single switch, and preferably in a high efficiency design that has a relatively low total size, while still allowing simple access by fibers to a closing photoconductive switch that actuates the bipolar pulse generator.